Well, I can't cover all few hundred (or thousands) of them, but customization is no secret.
A few members who say it is a myth or who thinks it is illegal or what not might only have 'heresy" at most. But I have seen with my own eyes and felt in my own hand.
One of the players my company sponsored was offered few blades to test, include a customized version of what she has been using previously. They said that customized blade is not suited for the rubbers we choose and it doesn't make any technical sense to pair them. End of the day, the player did not choose that blade and went for one with better technology.
Who is this player? at best she was world 300~400 and received customized blade as an option.
Played a little bit in France, but due to unforeseen circumstance, she couldn't continue her road to stardom.
She was one of my Olympic hopefuls back in the day, but right now she is an airforce pilot and I am proud of her.
(I have achieved most of my checklists since being involved in the sport for other than myself dating back to 2012, and helping get a player to the Olympics is one of those unticked boxes, sadly)
Customized blade is no secret - Butterfly own website on its sponsored players has so many players using "custom alc", "custom zlc" etc. Any doubters that customized equipment is not available can just search Butterfly and you can see for yourself.
Then talking about rubbers, it is no secret that DHS makes customize rubbers, and they even commercialize them in retail packaging.
There are many forum members (not necessary only on this forum, but including in China) that says its nonsense, but I have DHS distribution price list and any DHS distributor can tell you the sku number and are able to order them.
Next, many brands who sponsor players, guess what, the rubbers don't come in "commericial packaging". We can call it bulk packaging if you want to call it like that. I know few players that are stars (including rising stars) that to get customized sponges (other than DHS). For example, T05 with harder sponge back then, and that led to T05 Hard today. I know at least 3 other brands other than DHS that did some customization before. I can't say all the brands do it, I do know world ranked sponsored players also receiving commercial packaging, but I would believe they wouldn't just get from any random batch, careful selection should be no brainer.
Now onto boosters
Do they really need boosters?
Yes, many players grew up with boosters, it is just part of the gluing process now.
Speed glue days - every pro and semi pro uses it, so why not boosters in today's era? I won't get into the technicality of legality aspect, but the game is slower due to regulation updates over the decades and everyone needs to make it faster and if you not going to do it, you in an disadvantage.
I know way more people using boosters (where I have they contact number in my phone) then people not using boosters.
There are also very different boosters brands out there. Only a few is known to the west (from what I can gather on this forum)
There are also many players who have they own "formula" of using boosters. They will use on both DHS and non DHS rubbers.
The gluing (and booster) used will also depend on the playing hall/environment.
Even players like Dima has openly said he will use different layers of glues and sponge hardness in summer vs in winter or bigger or smaller hall. I assume that video is seen by the masses, so I'm just highlight that different "gluing" habits for the player do exist.
So at the end of the day, I will leave it to you all that equipment is a lot more technical than you think. It is actually so technical that I feel I have little knowledge of it.
But then, in this forum, there are many who think they know more. I just see them as trolling from the truth.
I thought I knew alot, until I physically felt them myself and the more I engage in these circles, the more I can feel my lack of knowledge of the topic. I am always learning something new every day.
Technical skills is very important, I would say forumers should not bother about equipment and focus on getting the basics right first.
But for the elite, it shouldn't surprised you that these brands will do everything they can do, to help the players be more complete and customization is really the least they can do.